linux-kernel - [PATCH 3.16 059/410] KVM/x86: Remove indirect MSR op calls from SPEC

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Message-ID: <lsq.1528380321.141806436@decadent.org.uk>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "David Woodhouse" <dwmw@...zon.co.uk>,
        "Jim Mattson" <jmattson@...gle.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        kvm@...r.kernel.org, "KarimAllah Ahmed" <karahmed@...zon.de>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Radim Krčmář" <rkrcmar@...hat.com>
Subject: [PATCH 3.16 059/410] KVM/x86: Remove indirect MSR op calls from
 SPEC_CTRL

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@...hat.com>

commit ecb586bd29c99fb4de599dec388658e74388daad upstream.

Having a paravirt indirect call in the IBRS restore path is not a
good idea, since we are trying to protect from speculative execution
of bogus indirect branch targets.  It is also slower, so use
native_wrmsrl() on the vmentry path too.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: KarimAllah Ahmed <karahmed@...zon.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kvm@...r.kernel.org
Fixes: d28b387fb74da95d69d2615732f50cceb38e9a4d
Link: http://lkml.kernel.org/r/20180222154318.20361-2-pbonzini@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/svm.c | 7 ++++---
 arch/x86/kvm/vmx.c | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -36,6 +36,7 @@
 #include <asm/desc.h>
 #include <asm/debugreg.h>
 #include <asm/kvm_para.h>
+#include <asm/microcode.h>
 #include <asm/nospec-branch.h>
 
 #include <asm/virtext.h>
@@ -3967,7 +3968,7 @@ static void svm_vcpu_run(struct kvm_vcpu
 	 * being speculatively taken.
 	 */
 	if (svm->spec_ctrl)
-		wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
 
 	asm volatile (
 		"push %%" _ASM_BP "; \n\t"
@@ -4077,10 +4078,10 @@ static void svm_vcpu_run(struct kvm_vcpu
 	 * save it.
 	 */
 	if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))
-		rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+		svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
 	if (svm->spec_ctrl)
-		wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
 
 	/* Eliminate branch target predictions from guest mode */
 	vmexit_fill_RSB();
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -46,6 +46,7 @@
 #include <asm/perf_event.h>
 #include <asm/debugreg.h>
 #include <asm/kexec.h>
+#include <asm/microcode.h>
 #include <asm/nospec-branch.h>
 
 #include "trace.h"
@@ -7542,7 +7543,7 @@ static void __noclone vmx_vcpu_run(struc
 	 * being speculatively taken.
 	 */
 	if (vmx->spec_ctrl)
-		wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
 
 	vmx->__launched = vmx->loaded_vmcs->launched;
 	asm(
@@ -7673,10 +7674,10 @@ static void __noclone vmx_vcpu_run(struc
 	 * save it.
 	 */
 	if (!msr_write_intercepted_l01(vcpu, MSR_IA32_SPEC_CTRL))
-		rdmsrl(MSR_IA32_SPEC_CTRL, vmx->spec_ctrl);
+		vmx->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
 	if (vmx->spec_ctrl)
-		wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
 
 	/* Eliminate branch target predictions from guest mode */
 	vmexit_fill_RSB();